Air Compressor Problem - Motor Stalls

I'm having a problem with my 20 gallon, single stage electric air
compressor. It's acting like the motor is underpowered - it pumps up
to about 95 psi ok, but then the motor stalls. The unloader bleeds the
pressure off, the motor restarts, runs for a couple of seconds, and
then stops again...repeat...repeat...

It worked fine for years (The pressure switch would shut it down at
about 120 psi) but over the past few months, it's gotten worse and
worse, and now will only make about 90-95 psi before the motor stalls.

I cleaned and lubricated the compressor itself, and it spins freely
and doesn't appear to be binding or otherwise have excessive friction.
The check valve/unloader is working and the piping is all open and
clear.

It seems like the electric motor (1/3 hp) just no longer has the oomph
it used to. It starts up fine, no humming, no smoking, no bad smells,
no clunks. It just doesn't seem to have enough running torque to
handle the load like it did before.

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On Thu, 04 Mar 2010 05:13:31 GMT, d (Sparks
Fergusson) wrote:
>
>I'm having a problem with my 20 gallon, single stage electric air
>compressor. It's acting like the motor is underpowered - it pumps up
>to about 95 psi ok, but then the motor stalls. The unloader bleeds the
>pressure off, the motor restarts, runs for a couple of seconds, and
>then stops again...repeat...repeat...

Bad pressure switch. The unloader is part of the pressure switch so if
it is being activated, the pressure switch is 'saying' that the
pressure is sufficient. Maybe it is just mis-adjusted.
>
>It worked fine for years (The pressure switch would shut it down at
>about 120 psi) but over the past few months, it's gotten worse and
>worse, and now will only make about 90-95 psi before the motor stalls.

Check the adjusting screws, and reset the cutoff back to 120 PSI.
Confirm the cuton is at 95 PSI.
>...

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In article <-september.org>, d (Sparks Fergusson) wrote:
>
>I'm having a problem with my 20 gallon, single stage electric air
>compressor. It's acting like the motor is underpowered - it pumps up
>to about 95 psi ok, but then the motor stalls. The unloader bleeds the
>pressure off, the motor restarts, runs for a couple of seconds, and
>then stops again...repeat...repeat...
>
>It worked fine for years (The pressure switch would shut it down at
>about 120 psi) but over the past few months, it's gotten worse and
>worse, and now will only make about 90-95 psi before the motor stalls.
>
>I cleaned and lubricated the compressor itself, and it spins freely
>and doesn't appear to be binding or otherwise have excessive friction.
>The check valve/unloader is working and the piping is all open and
>clear.
>
>It seems like the electric motor (1/3 hp) just no longer has the oomph
>it used to. It starts up fine, no humming, no smoking, no bad smells,
>no clunks. It just doesn't seem to have enough running torque to
>handle the load like it did before.
>
>Anyone have any ideas?
>

Check the line voltage while opperating at the motor.
I can do that stall with a long extension cord.

In article <hmohsd$30o$>, (GregS) wrote:
>In article <-september.org>,
> d (Sparks Fergusson) wrote:
>>
>>I'm having a problem with my 20 gallon, single stage electric air
>>compressor. It's acting like the motor is underpowered - it pumps up
>>to about 95 psi ok, but then the motor stalls. The unloader bleeds the
>>pressure off, the motor restarts, runs for a couple of seconds, and
>>then stops again...repeat...repeat...
>>
>>It worked fine for years (The pressure switch would shut it down at
>>about 120 psi) but over the past few months, it's gotten worse and
>>worse, and now will only make about 90-95 psi before the motor stalls.
>>
>>I cleaned and lubricated the compressor itself, and it spins freely
>>and doesn't appear to be binding or otherwise have excessive friction.
>>The check valve/unloader is working and the piping is all open and
>>clear.
>>
>>It seems like the electric motor (1/3 hp) just no longer has the oomph
>>it used to. It starts up fine, no humming, no smoking, no bad smells,
>>no clunks. It just doesn't seem to have enough running torque to
>>handle the load like it did before.
>>
>>Anyone have any ideas?
>>
>
>Check the line voltage while opperating at the motor.
>I can do that stall with a long extension cord.
>
>greg

It's an AC induction motor, so no brushes. Could it be a capacitor
issue?
>Does the unloader bleed the entire tank off? If so, then the check valve is
>probably bad.

It's a combination check/unloader valve. I cleaned and lubricated it,
and it appears to be working fine. The tank holds pressure - the
unloader just vents the tube between the tank and the compressor.
>It could also be that your shutoff set point has self
>adjusted back.

Good thought, but the pressure switch seems to be functioning well. I
am getting around the problem by turning down the pressure below the
point where the motor stalls. But, that's only about 90 psi, which is
not as much as I'd like. Plus, the problem seems to be getting worse.

PeterD <> wrote:
>On Thu, 04 Mar 2010 05:13:31 GMT, d (Sparks
>Fergusson) wrote:
>
>>
>>I'm having a problem with my 20 gallon, single stage electric air
>>compressor. ...
>
>Bad pressure switch. The unloader is part of the pressure switch so if
>it is being activated, the pressure switch is 'saying' that the
>pressure is sufficient. Maybe it is just mis-adjusted.

Actually, it's a mechanical unloader (combination check
valve/unloader, which I have already cleaned and lubricated.) It seems
to be working well.
>Check the adjusting screws, and reset the cutoff back to 120 PSI.
>Confirm the cuton is at 95 PSI.

The pressure swicth seems to be working fine. If I turn down the
pressure adjustment, I can get the contactor to turn off the motor
before it stalls, but that's only 90-95 psi or so. If I adjust it
higher, the motor is unable to turn the compressor if the pressure is
more than 95-100psi. It's definitely the motor stalling, not the
pressure switch opening.

(GregS) wrote:
>In article <hmohsd$30o$>, (GregS) wrote:
>>Check the line voltage while opperating at the motor.
>>I can do that stall with a long extension cord.
>>
>>greg
>
>Is it oiless ?If so, check the bearing.
>
>greg

Line voltage is OK, about 123 volts. It drops to around 121 volts when
the motor stalls. Voltage drop across the pressure switch is minimal
(less than a volt.) I'm not using an extension cord.

The compressor is oil filled, and has oil in it (although it is rather
old oil, come to think of it.) But, I can easily turn the compressor
over by hand and it feels like it's moving freely, with no excess
friction or binding.

In article <-september.org>, d (Sparks Fergusson) wrote:
>Bennett Price <> wrote:
>
>>> Thanks!
>>Do you know for sure that your gauge is correct? Maybe the compressor
>>and pressure switch are fine.
>
>Well, it's been working for a long time, but over the past few months
>has been exhibiting the stalling issue.
>
>I guess the guage could be wrong, but I kind of know what 120psi
>"feels like" and it's not getting up to what it used to, either by the
>guage or by feel.

The compressor speed does not slow down normally, it just starts to
sound a bit different under load.

I measured about 5 amps at startup (0 psi) rising to close to 6 when
it stalls. When it stops turning, the current actually drops back
closer to 5 amps, then increases as the motor starts turning again.

The motor is also hot to the touch after pumping all the way up. I can
hold my hand on it for maybe 6 or 8 seconds. I don't know if that's
different from how it used to be, though.

Alan Douglas <> wrote:
>Assuming it's a 120V/240V motor connected for 120, can you check to
>see if both run windings are actually connected? Perhaps a nut is
>working loose on the terminal plate inside the motor.

Hmm, you might have something, there! This motor is probably 15+ years
old, and has never had anything done to it. Could corrosion and/or
loose connections account for the lack of power? I can certainly try
cleaning and tightening anything I can get to.

"William R. Walsh"
<> wrote:
>Hi!
>
>You should check the pressure switch contacts to be sure they aren't
>burned. If they look OK, check the wiring leading to the compressor.
>Perhaps something is wrong there. (Be sure you shut the power off FIRST
>or you could have a shocking experience.)

Pressure switch contacts look OK, and there's minimal voltage drop
across under load. Wiring looks OK, too.
>Failing all of that, I'd check to see if the motor uses a run capacitor.
>If it does, the capacitor is probably bad.

There is a capacitor, but I'm not sure exactly what it does. I don't
have a wiring diagram and can't find any info on the Manufacturer's
website (GE.) I'll try to check the capacitor as best I can.

Could a capacitor issue cause the motor to start fine, but not have
enough power when running?

Sparks Fergusson wrote:
> Meat Plow wrote:
>
>
>>What kind of motor is this? I didn't see you mention that. A 1/3 horse
>>induction motor should not draw 1.5 amps with no load.
>
>
> It's some sort of GE induction motor. I have the model number, but I
> can't find anything about it on the GE website or Google.
>
> What sort of problems would high no-load amp draw suggest?
Bad bearings..
and if it's a single phase motor.. check the starter cap, if it
has one. most likely not much good any more..

Also, you may have a centrifugal switch in the motor that isn't
closing its contacts. Or, you could have an open winding!..

>>Assuming it's a 120V/240V motor connected for 120, can you check to
>>see if both run windings are actually connected? Perhaps a nut is
>>working loose on the terminal plate inside the motor.
>
>Hmm, you might have something, there! This motor is probably 15+ years
>old, and has never had anything done to it. Could corrosion and/or
>loose connections account for the lack of power? I can certainly try
>cleaning and tightening anything I can get to.

None of the other suggestions I've read, fit the symptoms. First
would be low voltage to the motor under load, but you've already
checked that. The starting capacitor is out of the circuit when the
motor is up to speed. There's nothing left in circuit but the two run
windings, wired in parallel.

On Sat, 06 Mar 2010 09:09:57 -0500, Alan Douglas
<> wrote:
>>>Assuming it's a 120V/240V motor connected for 120, can you check to
>>>see if both run windings are actually connected? Perhaps a nut is
>>>working loose on the terminal plate inside the motor.
>>
>>Hmm, you might have something, there! This motor is probably 15+ years
>>old, and has never had anything done to it. Could corrosion and/or
>>loose connections account for the lack of power? I can certainly try
>>cleaning and tightening anything I can get to.
>
>None of the other suggestions I've read, fit the symptoms. First
>would be low voltage to the motor under load, but you've already
>checked that. The starting capacitor is out of the circuit when the
>motor is up to speed. There's nothing left in circuit but the two run
>windings, wired in parallel.
>
>Alan

And all those replies ignore the fact the unloader is operating (at a
wrong, low pressure) which certainly doesn't point an evil finger at
the motor at all...